Carbon dioxide sequestration of concrete slurry waste and its valorisation in construction products

• Concrete slurry waste was recycled and reused in construction products.
• Concrete waste was considered as CO2 capture and storage medium.
• Carbon capture construction products were made of concrete wastes.
• The strength of carbonated mixture was as a power function of CO2 uptake.

This paper aimed to investigate the CO2 sequestration potential of concrete slurry waste (CSW) and its valorisation with fine recycled concrete aggregates (FRCAs) for the production of sustainable construction products by direct gas-solid mineral carbonation. Concrete slurry waste (CSW) with rich calcium and silicate phases is a by-product waste generated from concrete production in concrete batching plants. The CO2 sequestration extent achievable by CSW, FRCAs and their mixture, as well as the mechanical and durability properties of the mixture were evaluated in this study. It was found that the gas-solid carbonation mechanism of CSW and its mixture followed unreacted core model where a fast kinetically controlled process initially took place, then followed by a slow diffusion-controlled reaction process. Over 75% of the experimental CO2 uptake by CSW, FRCAs and their mixture occurred in less than 3-h carbonation and the CSW was able to sequestrate 110 g CO2 per kg dry mass after 7 days. Subjected to mineral carbonation, the mixture prepared with CSW and FRCAs quickly gained strength in a few hours and suffered lower drying shrinkage. Its strength development followed a power function of CO2 uptake, which was attributed to the gradual reduction in porosity with mineral carbonation. Furthermore, lifecycle assessment indicated that the production of the studied mixture as partition wall blocks was carbon neutral and environmentally sustainable due to CO2 capture and storage in concrete wastes.